The present invention relates to a piezoelectric/electrostrictive device having a movable portion to be operated based on a displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting a displacement of the movable portion by the piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance and can efficiently operate the movable portion in a large magnitude.
Recently, in a field of optics or magnetic recording, precision machining, or the like, a displacement element capable of adjusting an optical path length and a position in sub-micron order has been required, and development has progressed of a displacement element utilizing a displacement due to the inverse piezoelectric effect or electrostrictive effect obtained when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric substance or the like). For example, as shown in FIG. 2, a piezoelectric actuator 21 in which a fixing portion 25 and a movable portion 24 and a bridge beam 26 connecting therewith are integrally formed by providing a hole 28 on a board-like body composed of a piezoelectric/electrostrictive material, and an electrode layer 22 is further provided on the bridge beam 26, is disclosed in JP-A-10-136665.
In the actuator 21, when a voltage is applied to an electrode layer 22, the movable portion 24 can have an arc-shaped displacement or a rotational displacement in the plane of the board-like body, since the bridge beam 26 expands or contracts by the inverse piezoelectric effect or electrostrictive effect in a direction connecting the fixing portion 25 with the movable portion 24.
On the other hand, JP-A-63-64640 discloses a technique related to an actuator using a bimorph, wherein the bimorph is provided with divided electrodes such that a divided electrode is selected to drive the actuator to perform precise alignment at a high speed. For example, the specification shows in FIG. 4 a structure which uses two bimorphs positioned opposing to each other.
However, the actuator 21 has a problem that an operational quantity of the movable portion 24 is small, since the displacement in an expanding or contracting direction (namely, the in-plane direction of the board-like body) of a piezoelectric/electrostrictive material is transmitted per se to the movable portion.
Further, the actuator 21 has another problem that the actuator 21, having all the parts thereof constituted with a piezoelectric/electrostrictive material which is fragile and comparatively heavy, is low in mechanical strength, and inferior in handling property, impact resistance and humidity resistance, and further the actuator 21 per se is heavy and is easily influenced by a harmful vibration, for example, residual vibration or vibrational noise during high speed operation.
In order to solve above-described problems of the actuator 21, a proposition is made that a hole 28 is filled with an elastic filler. However, it is apparent that efficiency of the displacement due to the inverse piezoelectric effect or the electrostrictive effect is lowered when the filler is added.
On the other hand, what is shown in FIG. 4 of JP-A-63-64640 is, in bonding of an intermediary member 3 and a bimorph, a bonding of a site without the divided electrodes with the intermediary member, and therefore an advantage of the divided electrodes cannot be utilized at the bonded site. In other words, merely a site of the bimorph which is not a displacement generating portion is bonded. Further, on the other hand, a bonding formed at a bonding site of a head and the bimorph is similar. As a result, a bending displacement of the bimorph is developed toward an inner space between the intermediary member and the head, and the structure is not a type where the head per se is given an operation for effective displacement toward the outside space. In addition, the actuator disclosed in JP-A-63-64640 has a structure where a displacement generating member and a so-called frame member (an intermediary member or the like) are prepared separately, and adhered mutually to unite, thus the structure is liable to change over time the bonding condition of the frame and the bimorph, and also liable to cause drifting of the displacement, exfoliation, or the like. Further, a structure with an adhesive intervened at the bonding site of the bimorph with the intermediary member and at the bonding site of the head with the bimorph, namely at a holding portion of a displacement member, is lower in stiffness at the holding portion per se, thus making it difficult to increase a resonant frequency required for high speed operation.
The present invention is made in view of such problems in the conventional art, and an object thereof is to provide a displacement element which can largely operate a movable portion, and is hardly influenced by a harmful vibration in operation, capable of a high speed response, high in mechanical strength, and superior in handling property, impact resistance, and humidity resistance, as well as a sensor element capable of detecting a vibration of the movable portion in fine precision, and methods of fabricating the elements.